1. Field of the Invention
The present invention relates to a decorative laminate, a decorative laminate board as well as methods for producing the decorative laminate and decorative laminate board.
2. Brief Description of Related Art
Decorative laminates are being increasingly used in the field of floor coverings, work tops and table tops. Given the fields of application, properties such as abrasion resistance and wear resistance are of prime importance for the quality of such a decorative laminate and decorative laminate board. In addition, the properties that account for an optical impression of a patterned laminate or a surface of the decorative laminate, such as transparency and colour impression, are of particular relevance. Decorative laminate boards commonly comprise three main components: a protective layer (uppermost layer); a decorative layer having a pattern, which is covered by the protective layer; and a supporting substrate for supporting the protective layer and the decorative layer. Therefore, the properties of the protective layer or uppermost layer, respectively, are particularly relevant for an overall quality of the decorative laminate.
Conventionally, a so-called “overlay” is disposed on top of a decorative web, which overlay is a high-quality covering web or coating web made of paper which is impregnated with a resin and becomes transparent during the pressing process. As part of past efforts to improve an abrasion resistance of the decorative laminates and of the uppermost layer, in particular, hard particles, such as those made from silica, were incorporated into the uppermost layer. However, many manufacturers of decorative laminates encountered problems in achieving a homogeneous distribution of these particles in and on the coating web (overlay) and thus the uppermost layer.
This triggered a new trend of replacing covering webs with layers of synthetic resins comprising particles. To this effect, decorative laminates are conventionally manufactured by impregnating a paper web having a pattern thereon with a thermohardening resin and by either fully or partially hardening the impregnated paper web by application of pressure and heat, optionally together with a supporting web also impregnated with resin. Subsequently, the thus coated paper web is disposed on top of a supporting substrate, in case of a fully hardened decorative laminate by adhesive bonding or the like and in case of an only partially hardened decorative laminate by additional application of pressure and heat. Such decorative laminates tend to have a better transparency and thus convey a better optical impression of the pattern.
Continuous efforts are being made to improve properties of the protective layer, which are crucial for the properties of the entire decorative laminate, both with and without use of covering webs. As a result, many concepts for achieving protective layers of improved quality have been developed. These concepts mainly relate to the particles themselves, as well as the embedding of the particles in the synthetic resin. Use of hard particles in the production process created problems in that the tools used for application of pressure and heat, such as hot presses, were damaged by these new layers. This was attributed in particular to parts of the particles protruding and sticking out from a surface of the synthetic resin and resulted in increased wear of the tools.
Accordingly, efforts are made to improve embedding of the particles in the resin. Some approaches are based on an improvement of a distribution of the particles in the suspension used in the production process prior to its application, for instance by addition of α-cellulose, such as described in published patent application EP 0 732 449 A1.
Despite some success having already been achieved, there is still a need for decorative laminates and decorative laminate boards wherein embedding of the particles is improved. A fairly comprehensive review of the prior art may be found in European patent EP 0 875 399 B1, the content of which is incorporated by reference herein.